//飞入
$(document).ready(function () {
    $(window).scroll(function () {

        var a = $("#ln-p-box").offset().top;
        if (a >= $(window).scrollTop() && a < ($(window).scrollTop() + $(window).height())) {
            //alert("div在可视范围");

            var box = document.getElementById("ln-p-box");
            var aP= box.getElementsByTagName("p");

            for(var i=0;i<aP.length;i++){
                aP[i].className="on";
            }

        }
    });
});